Method and apparatus for setting up a relay link in a wireless communication system

ABSTRACT

A method and apparatus for setting up a relay link to transfer a data frame using a relay in a wireless communication system are provided. The relay link setup method of a source STA in a wireless communication system may include receiving capability information of at least one relay supporting station included in the wireless communication system from an access point (AP) or a personal basic service set (PBSS) central point (PCP), selecting one of the at least one relay supporting station as a relay station, using beam forming information among the source station, a destination station, and the at least one relay supporting station and the capability information, transferring a relay link setup request frame to the destination station, and receiving a relay link setup response frame that includes information on a relay link setup result from the destination station. The relay link setup request frame and the relay link setup response frame may pass through the relay station.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 15/676,295, filed onAug. 14, 2017, which is a continuation of U.S. application Ser. No.14/625,619, filed on Feb. 18, 2015 (now U.S. Pat. No. 9,736,886, issuedon Aug. 15, 2017), which is a continuation of U.S. application Ser. No.13/498,911, filed on Jun. 1, 2012 (now U.S. Pat. No. 8,989,078, issuedon Mar. 24, 2015), which is, in turn, a national stage of PCTapplication No. PCT/KR2010/006647, filed on Sep. 29, 2010. Furthermore,this application claims the foreign priority benefit of Koreanapplication No. 10-2009-0092715, filed on Sep. 29, 2009, Koreanapplication No. 10-2010-0011209, filed on Feb. 5, 2010, and Koreanapplication No. 10-2010-0025995, filed on Mar. 23, 2010. The disclosuresof these prior applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method and apparatus for setting up arelay link, and more particularly, to a relay link setup method andapparatus for transfer of a data frame using a relay in a wirelesscommunication system.

BACKGROUND ART

In a wireless communication system, for example a wireless local areanetwork (WLAN) environment of the institute of electrical andelectronics engineers (IEEE) 802.11, a data frame is transferred via anaccess point (AP) or directly by a peer-to-peer method. However,according to a general transfer method that uplinks and downlinks thedata frame with respect to the AP, other devices present in the network,such as stations, have to contend to obtain a channel. Accordingly, athroughput for data transfer may be reduced.

To solve such a limit, the data frame may be directly transferredbetween stations without passing through the AP through a direct linksetup (DLS) mode between the stations, such that a channel useefficiency may be at least doubled. However, even when the DLS mode isused, the throughput of the wireless network may be reduced when achannel state is deteriorated by multiple paths, attenuation,interference and the like. Also, in a case requiring a quality ofservice (QoS), such as multimedia streaming, a demanded QoS may not bemet.

In particular, the foregoing limits may become prominent in the WLAN,such as a 60 gigahertz (GHz) band that is currently standardized anduses millimeter waves. Millimeter wave communication may easily transferdata of several gigabits per second (Gbps) without high modulation,using a wide band such as a 2 GHz band. However, the millimeter wavecommunication may cause considerable loss of power due tocharacteristics of high frequency waves having a high degree ofstraightness. To overcome the loss of power, obtaining a high antennagain by collecting power in a particular direction is recommended,rather than all directions using a directional antenna.

However, when a line-of-sight (LOS) is not secured, signals may betransferred in a reflective manner. In this case, a signal transferdistance is increased, thereby increasing an attenuation loss.Consequently, loss by the reflection may be added. Furthermore, when aperson interrupts the LOS, a penetration loss becomes almost 20 decibels(dB) or more. Since an interior door or wall usually causes a greaterloss by interruption, it is difficult for signals to reach adestination.

As aforementioned, to overcome limits that may occur even with use ofthe DLS mode and the directional antenna, there is a need for a methodenabling relay of a frame through another station other than the AP inthe wireless network.

DISCLOSURE OF INVENTION Technical Goals

An aspect of the present invention provides a relay link setup methodand apparatus for transfer of a data frame using a relay in a wirelesscommunication system.

Other aspects and advantages of the present invention will be understoodfrom the following description, and become more apparent throughembodiments. Also, it will be understood that aspects and advantages ofthe present invention will be embodied by any means and combination ofthe means described in claims.

Technical Solutions

According to an aspect of the present invention, there is provided arelay link setup method of a source station in a wireless communicationsystem, the method including receiving capability information of atleast one relay supporting station included in the wirelesscommunication system from an access point (AP) or a personal basicservice set (PBSS) central point (PCP); selecting one of the at leastone relay supporting station as a relay station, using beam forminginformation among the source station, a destination station, and the atleast one relay supporting station and the capability information;transferring a relay link setup request frame to the destinationstation; and receiving a relay link setup response frame that includesinformation on a relay link setup result from the destination station.The relay link setup request frame and the relay link setup responseframe may pass through the relay station.

According to another aspect of the present invention, there is provideda relay link setup method of a relay station in a wireless communicationsystem, the method including performing beam forming, along with asource station; transferring, to the source station, channel measurementinformation according to the beam forming with the source station;receiving a relay link setup request frame from the source station andtransferring the relay link setup request frame to the destinationstation; and receiving a relay link setup response frame that includesinformation on a relay link setup result from the destination stationand transferring the relay link setup response frame to the sourcestation.

According to another aspect of the present invention, there is provideda relay link setup method of a destination station in a wirelesscommunication system, the method including performing beam forming alongwith a source station and at least one relay supporting station;transferring channel measurement information according to the beamforming with the source station and the at least one relay supportingstation to the source station; receiving a relay link setup requestframe from the source station; and transferring a relay link setupresponse frame that includes information on a relay link setup result tothe source station, wherein the relay link setup request frame and therelay link setup response frame pass through a relay station selected bythe source station from the at least one relay supporting station.

According to another aspect of the present invention, there is provideda source STA for performing relay link setup in the wirelesscommunication system, the source STA including a relay link setupapparatus according to an embodiment of the present invention mayinclude a first receiving unit to receive capability information of atleast one relay supporting STA included in the wireless communicationsystem from an AC or a PCP, a select unit to select one of the at leastone relay supporting STA as a relay STA using beam forming informationamong the source STA, the destination STA, and the at least one relaysupporting STA and the capability information, a transfer unit totransfer an RLS request frame to the destination STA, and a secondreceiving unit to receive an RLS response frame that includes relay linksetup result information from the destination STA. The RLS request frameand the RLS response frame may pass through the relay STA.

According to another aspect of the present invention, there is provideda relay STA for performing relay link setup in the wirelesscommunication system, the relay STA including a beam forming unit toperform beam forming along with a source STA, a first transfer unit totransfer channel measurement information according to the beam formingperformed with the source STA to the source STA, a second transfer unitto receive an RLS request frame from the source STA and transfer the RLSrequest frame to the destination STA, and a third transfer unit toreceive an RLS response frame that includes relay link setup resultinformation from the destination STA and transfer the RLS response frameto the source STA.

According to another aspect of the present invention, there is provideda destination STA for performing relay link setup in the wirelesscommunication system, the destination STA including a relay link setupapparatus may include a beam forming unit to perform beam forming alongwith a source STA and at least one relay supporting STA, a firsttransfer unit to transfer channel measurement information according tothe beam forming performed with the source STA and the at least onerelay supporting STA to the source STA, a receiving unit to receive anRLS request frame from the source STA, and a second transfer unit totransfer an RLS response frame that includes relay link setup resultinformation to the source STA. The RLS request frame and the RLSresponse frame may pass through the relay STA selected by the source STAfrom the at least one relay supporting STA.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a relay link setup method in a wirelesscommunication system according to an embodiment of the presentinvention;

FIG. 2 is a diagram illustrating a relay link setup method in a wirelesscommunication system according to another embodiment of the presentinvention;

FIG. 3 is a diagram illustrating a relay link setup method of a sourcestation (STA) in a wireless communication system according to anembodiment of the present invention;

FIG. 4 is a diagram illustrating a relay link setup method of a relaySTA in a wireless communication system according to an embodiment of thepresent invention; and

FIG. 5 is a diagram illustrating a relay link setup method of adestination STA in a wireless communication system according to anembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to embodiments of the presentinvention with reference to the accompanying drawings to fully explainthe present invention in such a manner that it may easily be carried outby a person with ordinary skilled in the art to which the presentinvention pertains. The foregoing aspects, features, and advantages willbe more apparent through the description that follows. Moreover,detailed descriptions related to well-known functions or configurationswill be omitted in order not to unnecessarily obscure subject matters ofthe present invention.

A wireless network complying with the institute of electrical andelectronics engineers (IEEE) 802.11 standard applies one of two modes,that is, an infrastructure basic service set (BSS) and an independentBSS (IBSS), so called ad hoc. The infrastructure BSS includes an accesspoint (AC) and a distribution system (DS) and generally uses the AP inalmost all communication processes including communication betweenstations (STA). The IBSS constructs a network including only STAswithout APs and does not allow an access through a DS.

Further, according to the infrastructure BSS, frames are received andtransferred generally through an AP. A new wireless local access network(WLAN) defines a direct link set (DLS) process for direct communicationbetween quality of service (QoS) STAs (QSTAs). According to the DLSprocess, the QSTA may set a direct link between the QSTAs by receivingand transferring a DLS request frame and a DLS response frame through aQoS AP or a legacy AP.

Additionally, according to the IBSS which does not include APs, allcommunication processes are performed in such a manner that a STA toperform communication makes a contention-based channel access such asdistributed coordination function (DCF), thereby performing directcommunication with a peer STA. According to a personal BSS (PBSS) whichis an example type of the IBSS, a PBSS central point (PCP) may functionsimilar to the AP.

Embodiments of the present invention will describe a method of receivingand transferring data using a relay rather than a DLS path or an APpassing path in a wireless communication system such as theinfrastructure BSS or the IBSS. That is, the embodiments of the presentinvention may be applied to a communication system that uses not onlythe AP but also the PCP or a network coordinator. Therefore,hereinafter, a description related to the AP may also be applied to thePCP or the network coordinator.

According to the embodiments of the present invention, a relay link maybe set up and data may be transferred through the relay link. For this,a relay STA for setting up the relay link is selected from STAs includedin a wireless communication system, and data is transferred through theselected relay STA. That is, data transferred from a source STA may bepassed through the selected relay STA and received by a destination STA.

Here, a process of recognizing directions of the respective STAs isnecessary to set up three links, that is, a source STA-relay STA (S-R)link, a relay STA-destination STA (R-D) link, and a sourceSTA-destination STA (S-D) link. Two methods may be suggested forrecognizing the directions of the STAs included in the wirelesscommunication system.

According to a first method adopted by a standardization organizationusing 60 GHz, two STAs may recognize the directions by performing beamforming through a directional antenna. Beam forming may besimultaneously performed with respect to the three links. However, beamforming requires a quantity of resources. Furthermore, a great amount oftime may be necessary since beam forming is performed withoutinformation on a physical position of an initial relay STA.

Accordingly, the directions of the STAs may be recognized through asecond method which performs beam forming by scanning in units of presetsectors. That is, a STA to perform communication may perform beamforming in a limiting manner through sector level sweep (SLS), therebyroughly recognizing the direction of the relay STA and setting acorresponding relay link. Additionally, a relay STA capable ofperforming data transfer more efficiently may be selected using channelmeasurement information obtained through beam forming.

Hereinafter, a relay link setup method according to the first methodwill be described with reference to FIG. 1. Also, a relay link setupmethod according to the second method will be described with referenceto FIG. 2. Although embodiments of the present invention will describethe relay link setup methods in the BSS, the embodiments are alsoapplicable to the IBSS such as a personal BSS (PBSS).

FIG. 1 is a diagram illustrating a relay link setup method in a wirelesscommunication system according to an embodiment of the presentinvention.

As shown in FIG. 1, the wireless communication system includes an AC101, a source STA 103, a relay STA 105, and a destination STA 107. Thesource STA 103 may transfer an association request frame to the AC 101according to passive scan in operation S101, and receive an associationresponse frame from the AC 101 in operation S103, thereby joining awireless network. The source STA 103 may receive a beacon frametransferred from the AC 101, thereby transferring the associationrequest frame. Alternatively, the source STA 103 may join the wirelessnetwork, by receiving and transferring a probe request frame and a proberesponse frame with respect to the AC 101 according to active scan. Therelay STA 105 and the destination STA 107 may join the wireless networkin the same manner as the source STA does.

Here, the STAs may transfer capability information of themselves to theAC 101 by including the capability information in the associationrequest frame or the probe request frame. The capability information mayrefer to relay capability information of the STA, which is necessary forrelay communication. That is, the STAs may inform the AC 101 as towhether to use relay, whether to support relay, and the like, throughthe capability information. The capability information may include atleast one selected from relay support information, relay useinformation, alternating current (A/C) power use information, mobilityinformation, relay function preference information, relay methodinformation, and cooperative communication support information. Also,the AC 101 may transfer capability information of the AC 101 to the STAsby including the capability information in the association responseframe, the probe response frame, or the beacon frame.

The relay capability information may be included in the associationrequest frame or the probe request frame in a format as shown in Table 1to Table 3 below. Table 1 indicates a format of the capabilityinformation. Table 2 indicates a capability information field. Table 3indicates a sub field in relation to Table 2. The relay capabilityinformation may include association identifier (AID) information of eachSTA.

TABLE 1 <Relay Capabilities element format> Element ID Length RelayCapability Info Octets: 1 1 2

TABLE 2 <Relay Capabilities info field> Relay Relay Relay A/C RelaySupportability Usability Permission Power Mobility Preference DuplexCooperation Bit B0 B1 B2 B3 B4 B5 B6-B7 B8

TABLE 3 <subfields of the relay capabilities info filed> SubfieldDefinition Encoding Relay Indicates that STA is Set to 1 if STA is relaySupportability capable of relaying via support capable. itself bytransmitting and Otherwise set to 0 receiving frames between a pair ofother STAs. A STA capable of relaying support is named “relay STA”.Relay Usability Indicates that STA is Set to 1 if STA is relay capableof using frame- usable capable. Otherwise relaying through a relay setto 0 STA. Relay Permission Indicates that PCP/AP Set to 0 by PCP/AP ifnot permits when a pair of permission. Set to 1 by if STAs exchange datavia permission relay STA A/C Power Indicates that relay STA Set to 1 ifrelay STA is is capable of obtaining capable of being supplied A/C powerby A/C power. Otherwise set to 0 Mobility Indicates that relay STA Sotto 1 if relay STA is is capable of support capable of support mobility.mobility Otherwise set to 0 Relay Preference Indicates that a STA is Setto 1 if a STA is desirable to become RSS desirable to be RSS. ratherthan RUS Otherwise set to 0 Duplex Indicates whether a STA Set to 01 ifrelay STA is is capable of FD/AF or not capable of HD/DF but HD/DF. onlycapable of FD/AF. Set to 10 if relay STA is capable of HD/DF but notcapable of FD/AF. Set to 11 if relay STA is capable of both HD/DF andFD/AF. 00 is reserved. Cooperation Indicates whether a STA Set to 1 if aSTA supports is capable of supporting Link cooperating. Set to 0Link-switching or Link- either if a STA supports cooperating.Link-switching, or if Duplex is set to 01.

The ‘Relay Supportability’ field that corresponds to the relay supportinformation may indicate whether an STA is capable of relaying by usinga value of 0 or 1.

The ‘Relay Usability’ field that corresponds to the relay useinformation may indicate whether the STA is capable of transferring aframe through relay by using a value of 0 or 1. In case of directionalcommunication such as millimeter wave communication, the ‘RelayUsability’ field may imply capability of searching for not only aline-of-sight (LOS) but also a relay STA and performing directionalcommunication in the corresponding direction.

The ‘Relay Permission’ field may indicate whether relay communication ofthe AC 101 is permitted in the BSS which includes the AC 101.

The ‘A/C Power’ field that corresponds to the A/C power use informationmay indicate whether the AC 101 or the STA receives power from an A/Cpower source by using a value of 0 or 1.

The ‘Mobility’ field that corresponds to the mobility information mayindicate whether the AC 101 or the STA is fixed or mobile by using avalue of 0 or 1.

The ‘Relay Preference’ field that corresponds to the relay functionpreference information may indicate whether the STA will function mainlyas the relay STA 105, by using a value of 0 or 1. When the ‘RelayPreference’ field is 1, the corresponding STA is preferred to functionmainly as the relay STA 105.

The ‘Duplex’ field that corresponds to the relay method information mayindicate whether the STAs will use a full duplex amplify-and-forward(FD/AF) relay method or a half duplex decode-and-forward (HD/DF) relaymethod for communication. When the ‘Duplex’ field is 01, the relay STA105 may support both FD/AF and HD/DF. When the ‘Duplex’ field is 10, therelay STA 105 may support HD/DF. When the ‘Duplex’ field is 11, therelay STA 105 may support FD/AF.

At last, the ‘Cooperation’ field that corresponds to the cooperativecommunication support information may indicate whether the STA will useonly one or both of a direct link and a relay link, by using a value of0 or 1. When the ‘Cooperation’ field is 1, the STA may be a linkcooperation type that uses both of the direct link and the relay link.When the ‘Cooperation’ field is 1, the STA may be a link switching typewhich uses the direct link or the relay link according to a link status.The ‘Cooperation’ field is effective only in the HD/DF relay method.

When the AC 101 permits relay communication, the source STA 103 maytransfer a relay search request frame for searching for a relaysupporting STA to the AC 101, in operation S105. Here, the source STA103 may confirm whether the AC 101 permits relay communication using thecapability information of the AC 101 transferred from the AC 101.

The AC 101 may transfer a relay search response frame that includes thecapability information of the STA included in the BSS to the source STA103, in operation S107. As aforementioned, the AC 101 may receive thecapability information from the STA included in the BSS.

The source STA 103 may select the relay STA by receiving the STAinformation of the relay STA 105 from the AC 101. That is, at least onerelay supporting STA that supports a relay function may be included inone BSS. The source STA 103 may select the relay STA for setting a relaylink from the at least one relay supporting STA. According to theembodiment shown in FIG. 1, a single relay supporting STA is included inthe BSS as the relay STA 105 and a relay link is set with respect to therelay STA 105. Hereinafter, a method of selecting the relay STA 105 willbe described.

For example, presuming that a fixed STA has a higher priority than amobile STA, that a STA using A/C power has a higher priority than a STAusing battery power, and that the ‘Mobility’ field has a higher prioritythan the ‘A/C Power’ field, the priority may be determined as ‘FixedSTA>Mobile STA & A/C Power STA>Mobile STA & Battery Power STA.’ In thiscase, the source STA 103 may select a laptop rather than a mobile phoneand select a television (TV) rather than a laptop as the relay STA.

The priority may be determined as shown in Table 4 below. That is, thepriority may be determined in order of a channel status, the relayfunction preference information, the A/C power use information, and themobile information. Since a physical position of the relay STA 105 is aninfluential factor for the communication performance, the channel statusamong STAs may be given highest priority in selection of the relay STA105. Information on the channel status may be obtained through beamforming that will be described later or scanning that will be describedwith reference to FIG. 2.

TABLE 4 <Relay STA selection criteria> Order Information Note 1 Channelstatus Higher value is preferred. It is obtained by STA Scan operation.2 Relay preference field = 1 Relay preference field = 1 is preferred. 3A/C power field = 1 A/C power field = 1 is preferred. 4 Mobility field =0 Mobility field = 0 is preferred.

Next, the source STA 103 may perform relay association with respect tothe selected relay STA 105. The source STA 103 may transfer a relayassociation request frame to the AC 101, in operation S109. Here, DLSmay be completed between the source STA 103 and the destination STA 107.That is, the relay association may refer to a process of performinginitialization for having data to be transferred between the source STA103 with which DLS is completed and the destination STA 107 bypassingthe relay STA 105, and a process of performing beam forming of threelinks among the respective STAs, that is, the S-R link, the R-D link,and the S-D link.

The AC 101 may broadcast a relay association response frame to the STAin response to the relay association request frame, in operation S111.The AC 101 may reserve a section for the beam forming with respect tothe three links, and transfer the relay association response frame thatincludes information on a start address and duration of the reservedsection. Since beam forming needs to be performed with respect to all ofthe STAs 103, 105, and 107 included in the BSS, the AC 101 may broadcastthe relay association response frame. When resources are sufficient forallocation of the beam forming section, the AC 101 may allocate asection enabling beam forming of the three links simultaneously. Whenresources are insufficient, the AC 101 may separately allocate resourcesper link.

A format of the relay association request frame may be as shown in Table5. A format of the relay association response frame may be as shown inTable 6.

TABLE 5 Order Information 1 Category 2 Action 3 Dialog Token 4Destination Relay Usable STA N AID

TABLE 6 Order Information 1 Category 2 Action 3 Dialog Token 4 StatusCode 5 Relay Capable STA Info . . . . . . N + 4 Relay Capable STA Info

In Table 5, the ‘Category’ field may indicate millimeter wavecommunication. The ‘Action’ field may indicate frame types. The ‘DialogToken’ field may include a value selected by a STA that transfers arequest frame for distinction between request transaction and responsetransaction. The ‘Destination Relay Usable STA AID’ field may indicatean AID of a target destination STA. In FIG. 1, the target destinationSTA refers to the destination STA 107.

In Table 6, the ‘Status Code’ field may indicate status informationrelated to a relay search request. When the ‘Status Code’ field is 0,the relay search request may be successful. A next field following the‘Status Code’ field may include an address of the STA, the capabilityinformation, and relay link setup information with respect to anotherSTA. When the ‘Status Code’ field is 37, the relay search request may berejected. When the ‘Status Code’ field is 37, the relay search requestmay be rejected since the BSS does not include a relay supporting STA.The ‘Relay capable STA Info’ field may include the capabilityinformation described with reference to Table 1 to Table 3.

The ‘Action’ field value in Table 5 and Table 6 may be defined as shownin Table 7 below. An ‘Action’ field value of a frame format describedhereinafter may also be defined as shown in Table 7.

TABLE 7 <Relay Action Field Values> Action field value meaning 0 RelaySearch Request 1 Relay Search Response 2 Multi-Relays ChannelMeasurement Request 3 Multi-Relays Channel Measurement Report 4 RLSRequest 5 RLS Response 6 RLS Announcement 7 RLS Teardown 8 RelayAcknowledgment 9-255 Reserved

The STAs 103, 105, and 107 included in the BSS may perform beam formingusing information included in the relay association response frame inoperations S113, S115, and S117. When the section enabling beam formingof the three links simultaneously is allocated, the beam forming may beperformed in order of the S-R link, the R-D link, and the S-D link.Here, in operation S119, the destination STA 107 may transfer, to thesource STA 103, a multi-relays channel measurement report frame whichincludes channel measurement information according to the beam formingand internal angle information between a direction toward the relay STA105 and a direction toward the source STA 103. The channel informationaccording to the beam forming is related to the link between the relaySTA 105 and the destination STA 107 and the link between the source STA103 and the destination STA 107. The multi-relays channel measurementreport frame will be described in further detail with reference to FIG.2.

The source STA 103 may select the relay STA using a beam forming resultand the channel measurement information. In addition, the source STA 103may transfer, to the AC 101, a relay association report frame thatincludes information on a relay association result. Thus, the relay linksetup may be completed. Therefore, the source STA 103, the relay STA105, and the destination STA 107 may receive and transfer data using therespective links.

FIG. 2 is a diagram illustrating a relay link setup method in a wirelesscommunication system according to another embodiment of the presentinvention.

The relay link setup method of FIG. 2 is similar to the relay link setupmethod of FIG. 1. However, according to the relay link setup method ofFIG. 2, beam forming between STAs is performed through scanning in unitsof preset sectors and a relay link is set up through a relay link setup(RLS) request frame after the beam forming. Hereinafter, the relay linksetup method will be described in detail.

As shown in FIG. 2, the wireless communication system may include an AP201, a source STA 203, a relay STA 205, and a destination STA 207. Inthe same manner as in the embodiment of FIG. 1, the STAs 203, 205, and207 included in a BSS may access a wireless network, and the source STA203 obtains capability information of the STAs and the AP 201 includedin the BSS. That is, the source STA 203 may obtain the capabilityinformation by transferring a relay search request frame to the AP 201.

Next, the STAs 203, 205, and 207 included in the BSS may perform beamforming through scanning performed in units of preset sectors. The STAs203, 205, and 207 included in the BSS may perform scanning by sweepingthe preset sector using a quasi-omni antenna pattern and may recognizelocations relative to one another. Here, the direction toward each STAmay indicate a direction of the preset sector when only sector sweepingis performed during the scanning, or indicate a direction inferred froma weighting vector calculated through reception beam forming.

Here, the AP 201 may reserve relay scan with respect to the STA includedin the BSS. The relay scan refers to scanning in units of the presetsectors. The AP 201 may reserve the relay scan with respect to apredetermined scan section as the beam forming section of FIG. 1 isreserved, by broadcasting relay scan request frames. The relay STA 205may transfer the relay scan request frames to the source STA 203 and thedestination STA 207 in operations S201 and S203. The source STA 203 andthe destination STA 207 may transfer relay scan response frames to therelay STA 205 in operations S205 and S207, thereby performing scanning.

Through the scanning, channel measurement information may be obtainedwith respect to the three links, that is, the S-R link, the R-D link,and the S-D link. In addition, the source STA 203 may select a relay STAfrom at least one relay supporting STA using the channel measurementinformation. That is, the source STA 203 may select the relay STA havinghigh transfer efficiency using not only the received capabilityinformation but also the channel measurement information along with thecapability information.

The source STA 203 may transfer a multi-relays channel measurementrequest frame for requesting the channel measurement information to thedestination STA 207, in operation S209. The destination STA 207 maytransfer a multi-relays channel measurement report frame to the sourceSTA 203, in operation S211. Here, the source STA 203 may transfer themulti-relays channel measurement request frame also to the relay STA205.

The channel measurement information may include channel measurementinformation between the source STA 203 and the destination STA 207,channel measurement information between the relay STA 205 and thedestination STA 207, and internal angle information between the S-D linkand a link between the destination STA 207 and the relay supporting STA.When the relay STA 205 transfers the multi-relays channel measurementrequest frame to the source STA 203, the channel measurement informationmay include channel measurement information between the source STA 203and the relay STA 205, channel measurement information between the relaySTA 205 and the destination STA 207, and internal angle informationbetween the S-R link and the R-D link. When the BSS includes a pluralityof relay supporting STAs, the channel measurement information mayinclude information on all of the plurality of relay supporting STAs.

A format of the multi-relays channel measurement request format and aformat of the multi-relays channel measurement report frame may beconfigured as shown in Table 8 and Table 9, respectively. In Table 9, a‘Channel Measurement Info’ field may be a field including channelmeasurement information related to a channel with at least one STA. Aformat of the ‘Channel Measurement Info’ may be configured as shown inTable 10.

TABLE 8 <Multi-Relays Channel Measurement Request> Order Information 1Category 2 Action 3 Dialog Token

TABLE 9 <Multi-Relays Channel Measurement Report> Order Information 1Category 2 Action 3 Dialog Token 4 Channel Measurement Info 1 . . . . .. N + 3 Channel Measurement Info N

TABLE 10 <Channel Measurement Info field> Internal Peer STA AID SNRAngle Recommend Reserved Bits: B0-B7 B8-B15 B16-B22 B23 B24-B31

In Table 10, the ‘Peer STA AID’ field may indicate an AID of a STA thattransfers the multi-relays channel measurement report frame channelmeasurement information. The ‘SNR’ field may indicate a signal-to-noiseratio (SNR) value measured in the link. The ‘Internal angle’ field mayindicate the internal angle information. The ‘Recommend’ field mayindicate whether the link is recommended according to a channelmeasurement result. When the measured link is recommended, the‘Recommend’ field value may be set to 1.

The internal angle information between the S-D link and the link betweenthe source STA 203 and the relay supporting STA may be used to preventfollowing cases.

First, when only the channel measurement information is measured, a casein which a link between the source STA and the destination STA includesa relay STA vertically or horizontally disposed may be determined to bein a better location than a case in which the direct link does notinclude the relay STA. However, since a main purpose of using the relaylink is bypassing in case that the direct link is blocked, when therelay STA is present on or around the direct link, even the relay linkmay be blocked by a high probability when the direct link is blocked bya moving object. Therefore, such a case may be solved by measuring theinternal angle between the S-D link and the link between the source STA203 and the relay supporting STA, and selecting the relay supporting STAwhen the internal angle is larger than or equal to a predeterminedthreshold value.

Second, the relay STA 205 may particularly adopt a full duplex (FD)method since divergence by a positive feedback may be prevented when adata transferring direction and a data receiving direction are separatethan when the directions are identical. The data transferring directionand the data receiving direction may be identical although a transmitter(Tx) antenna, a receiver (Rx) antenna, and a radio frequency (RF) moduleare physically separated. The relay STA 205 may recognize theaforementioned state and inform the source STA 203 of the state, bysetting the ‘Recommend’ field to 0 when a dissipation degree is highalthough the internal angle is large. In addition, the internal angleinformation measured by the relay STA 205 and the destination STA 207may enable the source STA 203 to recognize locations of the relay STA205 and the destination STA 207 because the three links form a triangle.That is, since the source STA 203 may recognize the location of therelay STA 205 using the internal angle information, the source STA 203may be prevented from being located at a location that may block therelay STA 205 by a high probability although the internal angle islarge.

When the relay STA 205 is present on a direct link between the sourceSTA 203 and the destination STA 207, the direct link may be disconnectedby a high probability as a person passes by the source STA 203 and thedestination STA 207. Therefore, it is preferred that the relay STA 205is located diagonally. The source STA 203 may select an optimal relaySTA using the channel measurement information.

That is, as aforementioned, the source STA 203 may select the relay STA205 from the at least one relay supporting STA using the channelmeasurement information and the capability information.

When the relay STA is selected, the source STA 203 may transfer an RLSrequest frame to the destination STA 207 in operations S213 and S215.The destination STA 207 may transfer an RLS response frame that includesrelay link setup result information to the source STA 203 in operationsS217 and S219. That is, the destination STA 207 may transfer, to thesource STA 203, the RLS response frame that includes information onwhether the destination STA 207 succeeded or failed in the RLS, that is,whether the destination STA 207 participated in RLS, in operations S217and S219.

Here, the RLS request frame and the RLS response frame may pass throughthe relay STA 205. The relay STA 205 may also transfer the RLS responseframe that includes the relay link setup result information to thesource STA 203. RLS may be performed in a similar manner as DLS. In RLS,the relay STA 205 may perform the function of the AP of DLS.

The RLS request frame may include capability information and AIDinformation of the source STA 203, the relay STA 205, and thedestination STA 207, and may further include a relay transfer parameter.The relay transfer parameter may include at least one selected fromrelay method information, cooperative communication use information,transfer mode information according to use of the cooperativecommunication, data sensing time information indicating a deferred timecaused by link switching, frame exchange section information between thesource STA and the relay STA, and frame exchange section informationbetween the relay STA and the destination STA.

Formats of the RLS request frame, the RLS response frame, and the relaytransfer parameter may be configured as shown in Table 11 to Table 13.As shown in Table 12, the RLS response frame may also include thecapability information and the AID information of the source STA 203,the relay STA 205, and the destination STA 207. In Table 12, aDestination Status Code′ field may correspond to the relay link setupresult information of the destination STA 207. When the destination STA207 participates in RLS, the Destination Status Code′ may be set tozero. When the destination STA 207 does not participate in RLS, the‘Destination Status Code’ may be set to 37. A ‘Relay Status Code’ fieldcorresponding to the relay link setup result information of the relaySTA 205 may be set in the same manner as the ‘Destination Status Code.’

TABLE 11 <RLS Request> Order Information 1 Category 2 Action 3 DialogToken 4 Destination AID 5 Relay AID 6 Source AID 7 DestinationCapability Information 8 Relay Capability Information 9 SourceCapability Information 10 RLS Timeout Value 11 Relay Transfer ParameterSet

TABLE 12 <RLS Response> Order Information 1 Category 2 Action 3 DialogToken 4 Destination AID 5 Relay AID 6 Source AID 7 DestinationCapability Information 8 Relay Capability Information 9 SourceCapability Information 10 Destination Status Code 11 Relay StatusCode(Optional)

TABLE 13 <Relay Transfer Parameter Set IE> Element ID Length RelayTransfer Parameter Octets: 1 1 8

The relay transfer parameter may be configured as shown in Table 14.

TABLE 14 Link Data Duplex- Cooperation- Tx- Change Sensing First SecondMode Mode Mode Reserved Interval Time Period Period Reserved Bit B0 B1B2 B3-B7 B8- B16- B24- B40- B56-B63 B15 B23 B39 B55

The ‘Relay Transfer Parameter’ field may indicate a parameter necessaryfor setting a mode of the relay STA 205 that participated in RLS and fortransferring data.

The ‘Duplex-mode’ field may correspond to the relay method information.When the relay STA 205 supports the FD-AF, one of the FD relay methodand the HD relay method may be selected from the ‘Duplex-mode’ field.The ‘Duplex-mode’ field may be set to 0 when the relay STA 205 is to beoperated by HD-DF and set to 1 when the relay STA 205 is to be operatedby FD-AF.

The ‘Cooperation-mode’ field may correspond to the cooperativecommunication use information. A link-switching mode or alink-cooperating mode may be selected from the ‘Cooperation-mode.’ The‘Cooperation-mode’ field may be set to 0 when the relay STA 205 is to beoperated in the link-switching mode and set to 1 when the relay STA 205is to be operated in the link-cooperating mode. In addition, the‘Cooperation-mode’ field is valid when the relay STA 205 is in thelink-cooperating mode and the ‘Duplex-mode’ field is set to 0, and maybe ignored otherwise.

The ‘Tx-mode’ field may correspond to the transfer mode informationaccording to use of the cooperation communication. When the three STAsparticipating in RLS are operated in a normal mode, the ‘Tx-mode’ fieldmay be set to 0. When the three STAs participating in RLS are operatedin an alternation mode, the ‘Tx-mode’ field may be set to 1. The normalmode is used by only one of the direct link and the relay link. Thealternation mode is used by both of the direct link and the relay link.The ‘Tx-mode’ field is valid when the relay STA 205 is in thelink-switching mode and the ‘Duplex-mode’ field is set to 1, and may beignored otherwise.

The ‘Link Change Interval (LCI)’ field may correspond to the link switchsection information indicating the link switch section. The ‘LCI’ fieldmay indicate a section in which the link between the source STA 203 andthe destination STA 207 is switched. That is, the ‘LCI’ field may informa point of time for bypassing when data is bypassed to another pathsince a currently used path is blocked. A chance of switching the linkmay be given every LCI from an initial position of a reserved section.In one section, transfer to only one link is allowed. The data transferpath may be bypassed only at a point corresponding to every multiplenumber of the ‘LCI’ field value from the reserved time.

The ‘Data Sensing Time’ field may correspond to the data sensing timeinformation indicating the deferred time caused by the link switching.The ‘Data Sensing Time’ field may indicate time deferred while linkswitching is performed from a currently used LCI to a following LCI. The‘Data Sensing Time’ field may be used only in the normal mode, not inthe alternation mode. Under the HD-DF relay mode, the ‘Data SensingTime’ field may be used when the direct link is switched to the relaylink, but not used when the relay link is switched to the direct link.

The ‘First Period’ field may correspond to the frame exchange sectioninformation between the source STA 203 and the destination STA 207. Thatis, the ‘First Period’ field may indicate a section in which frames areexchanged between the source STA 203 and the destination STA 207 whenthe relay link is used under the HD-DF relay mode.

The ‘Second Period’ field may correspond to the frame exchange sectioninformation between the relay STA 205 and the destination STA 207. Thatis, the ‘Second Period’ field may indicate a section in which frames areexchanged between the relay STA 205 and the destination STA 207 when therelay link is used under the HD-DF relay mode, and all frame sectionsfor informing the source STA 203 of the status of the R-D link.

The relay transfer parameter may be updated even after the relay link isset. For example, when a channel environment is greatly changed afterthe relay transfer parameter is set, the ‘LCI’ field, the ‘First Period’field, and the ‘Second period’ may be changed. The updated relaytransfer parameter may be included in the RLS request frame andtransferred from the source STA 203.

According to the relay link setup result information, the source STA 203may transfer an RLS announcement frame that includes information onwhether the relay link setup is successful to the AC 201, in operationS221. The AC 201 receiving the RLS announcement frame may confirm thatthe RLS is successful. A format of the RLS announcement frame may beconfigured as shown in Table 14 below. The RLS announcement frame mayinclude AIDs of the source STA 203, the relay STA 205, and thedestination STA 207 that participated in RLS.

TABLE 15 <RLS Announcement> Order Information 1 Category 2 Action 3Status Code 4 Destination AID 5 Relay AID 6 Source AID

After the RLS announcement frame is transferred to the AC 201, beamforming may be performed again with respect to each of the three linksto increase throughput of data transfer. Here, the beam forming may beperformed in the same manner as described with reference to FIG. 1.Channel measurement information newly obtained during the beam formingmay be transferred to the source STA 203. In addition, the relaytransfer parameter may be updated.

In order to tear down the relay link, the source STA 203 may transfer arelay teardown frame to the relay STA 205, the destination STA 207, andthe AC 201. The relay teardown frame may be transferred to thedestination STA 207 passing through the relay STA 205. The relayteardown frame may include AID information of the source STA 203, therelay STA 205, and the destination STA 207. A format of the relayteardown frame may be configured as shown in Table 16.

TABLE 16 <RLS Teardown> Order Information 1 Category 2 Action 3 StatusCode 4 Destination AID 5 Relay AID 6 Source AID

In addition, the relay source STA 205 may transfer a relayacknowledgement frame to the source STA 203 in which RLS is completed,to inform whether the RLS announcement frame is successfully receivedfrom the destination STA 207 through the set relay link. The relayacknowledgement frame may use the HD-DF relay method and may be usedonly in the link-switching mode. A format of the relay acknowledgementframe may be configured as shown in Table 17. A ‘BA Control’ field, a‘BlockAck Starting Sequence Control’ field, and a ‘BlockAck Bitmap’field may be used when a ‘BlockAck’ field is used.

TABLE 17 <Relay Acknowledgement> Order Information 1 Category 2 Action 3BA Control(Optional) 4 BlockAck Starting Sequence Control(Optional) 5BlockAck Bitmap(Optional)

The relay link setup methods described with reference to FIGS. 1 and 2may be used together or wholly or partially altered and mixed. Forexample, beam forming through scanning in units of the preset sectorsmay be performed in the embodiment of FIG. 1. The beam forming as inFIG. 1 may also be performed in the embodiment of FIG. 2. The priorityas shown in Table 4 may be used also in the embodiment of FIG. 2.Hereinafter, a link setup method of the source STA, the relay STA, andthe destination STA of FIGS. 1 and 2 will be described.

FIG. 3 is a diagram illustrating a relay link setup method of a sourceSTA in a wireless communication system according to an embodiment of thepresent invention. As shown in FIG. 3, the relay link setup methodbegins from operation S301.

In operation S301, the source STA may receive capability information ofat least one relay supporting STA included in the wireless communicationsystem from an AC or a PCP. In detail, operation S301 may includetransferring, to the AC or the PCP, a relay search request frame forrequesting the capability information of the at least one relaysupporting station, and receiving a relay search response frame thatincludes the capability information of the at least one relay supportingstation from the AC or the PCP. The at least one relay supportingstation may transfer the capability information to the AC or the PCPwhen making an access to a wireless network.

In operation S303, the source STA may select one of the at least onerelay supporting STA as a relay STA using beam forming information amongthe source STA, the destination STA, and the at least one relaysupporting STA and the capability information of the at least one relaysupporting STA. Here, the beam forming may be performed as describedwith reference to FIG. 1 or through scanning in units of preset sectorsas described with reference to FIG. 2. The destination STA may performbeam forming along with the at least one relay supporting STA and thesource STA. The source STA may perform beam forming along with the atleast one relay supporting STA and the destination STA.

Further, operation S303 may include transferring a multi-relays channelmeasurement request frame for requesting channel measurement informationaccording to the beam forming to the destination STA, receiving amulti-relays channel measurement response frame that includes thechannel measurement information from the destination STA, and selectingthe relay station using the channel measurement information and thecapability information. The channel measurement information may includechannel measurement information between the source STA and thedestination STA, channel measurement information between the at leastone relay supporting STA and the destination STA, and internal angleinformation between a link between the source STA and the destinationSTA and a link between the destination STA and the at least one relaysupporting STA.

In operation S305, the source STA may transfer an RLS request frame tothe destination STA. In operation S307, the source STA may receive anRLS response frame that includes relay link setup result informationfrom the destination STA. Here, the RLS request frame and the RLSresponse frame may pass through the relay STA.

The RLS request frame may include capability information and AIDinformation of the source STA, the relay STA, and the destination STA,and a relay transfer parameter. The relay transfer parameter may includeat least one selected from relay method information, cooperativecommunication use information, transfer mode information according tothe cooperative communication use, link switch section informationdenoting a link switch section, data sensing time information denoting adeferred time caused by link switching, frame exchange sectioninformation between the source station and the relay station, and frameexchange section information between the relay station and thedestination station.

The relay link setup method according to the embodiment of the presentinvention may further include transferring the capability information ofthe source STA to the AC or the PCP. Here, the capability informationmay include at least one selected from relay support information, relayuse information, alternating current (A/C) power use information,mobility information, relay function preference information, relaymethod information, and cooperative communication support information.The capability information may be included in an association requestframe or a probe request frame.

Additionally, the relay link setup method may further includetransferring an announcement frame that includes information on successof relay link setup to the AC or the PCP according to the relay linksetup result information.

The relay link setup method may further include transferring a relayteardown frame for tearing down the relay link to the relay STA, thedestination STA, and the AC or the PCP. Here, the relay teardown framemay include AID information of the source STA, the relay STA, and thedestination STA. The relay teardown frame may be transferred to thedestination STA by passing through the relay STA.

FIG. 4 is a diagram illustrating a relay link setup method of a relaySTA in a wireless communication system according to an embodiment of thepresent invention. As shown in FIG. 4, the relay link setup method maybegin from operation S401. The relay STA in FIG. 4 may be theaforementioned relay supporting STA.

In operation S401, the relay STA may perform beam forming along with thesource STA. Here, beam forming may be performed in the same manner asdescribed with reference to FIG. 1 or through scanning in units ofpreset sectors as in FIG. 2. The relay STA may additionally perform beamforming along with the destination STA.

In operation S403, the relay STA may transfer channel measurementinformation according to the beam forming performed with the source STA.The relay STA may transfer the channel measurement information to thesource STA using a multi-relays channel measurement response frame.

In operation S405, the relay STA may receive an RLS request frame fromthe source STA and transfer the RLS request frame to the destinationSTA. The RLS request frame may include capability information and AIDinformation of the source STA, the relay STA, and the destination STA,and a relay transfer parameter related to a relay link. The relaytransfer parameter may include at least one selected from relay methodinformation, cooperative communication use information, transfer modeinformation according to the cooperative communication use, link switchsection information denoting a link switch section, data sensing timeinformation denoting a deferred time caused by link switching, frameexchange section information between the source station and the relaystation, and frame exchange section information between the relaystation and the destination station.

In operation S407, the relay STA may receive the RLS response frame thatincludes relay link setup result information from the destination STA,and transfer the RLS response frame to the source STA. The relay STA mayalso transfer the RLS response frame that includes the relay link setupresult information to the source STA in response to the received RLSrequest frame.

The relay link setup method may further include transferring thecapability information of the relay STA to an AC or a PCP. Thecapability information may include at least one selected from relaysupport information, relay use information, A/C power use information,mobility information, relay function preference information, relaymethod information, and cooperative communication support information.

In addition, the relay link setup method may include receiving a relayteardown frame for tearing down the relay link from the source station,and transferring the relay teardown frame to the destination station.The relay teardown frame may include AID information of the sourcestation, the relay station, and the destination station.

Operation S403 may be omitted from the relay link setup method of therelay STA. The source STA may select the relay STA using the channelmeasurement information transferred from the destination STA.

FIG. 5 is a diagram illustrating a relay link setup method of adestination STA in a wireless communication system according to anembodiment of the present invention. As shown in FIG. 5, the relay linksetup method begins from operation S501.

In operation S501, the destination STA may perform beam forming alongwith a source STA and at least one relay supporting STA. The beamforming may be performed in the same manner as in FIG. 1 or throughscanning in units of preset sectors as in FIG. 2.

In operation S503, the destination STA may transfer channel measurementinformation according to the beam forming performed with the source STAand the at least one relay supporting STA, to the source STA. In furtherdetail, operation S503 may include receiving a multi-relays channelmeasurement request frame for requesting the channel measurementinformation according to the beam forming from the source STA, andtransferring a multi-relays channel measurement response frame thatincludes the channel measurement information to the source STA. Thechannel measurement information may include channel measurementinformation between the source STA and the destination STA, channelmeasurement information between the at least one relay supporting STAand the destination STA, and internal angle information between a linkbetween the source STA and the destination STA and a link between thedestination STA and the at least one relay supporting STA.

In operation S505, the destination STA may receive an RLS request framefrom the source STA. The RLS request frame may include capabilityinformation and AID information of the source STA, the relay STA, andthe destination STA, and a relay transfer parameter. Here, the relaytransfer parameter may include at least one selected from relay methodinformation, cooperative communication use information, transfer modeinformation according to use of the cooperative communication, datasensing time information indicating a deferred time caused by linkswitching, frame exchange section information between the source STA andthe relay STA, and frame exchange section information between the relaySTA and the destination STA.

In operation S507, the destination STA may transfer an RLS responseframe that includes relay link setup result information to the sourceSTA. The RLS request frame and the RLS response frame may pass throughthe relay STA selected by the source STA from the at least one relaysupporting STA.

The relay link setup method may further include transferring thecapability information of the destination STA to an AC or a PCP. Thecapability information may include at least one selected from relaysupport information, relay use information, A/C power use information,mobility information, relay function preference information, relaymethod information, and cooperative communication support information.

In addition, the relay link setup method may further include receiving arelay teardown frame for tearing down the relay link from the sourcestation. The relay teardown frame may include AID information of thesource station, the relay station, and the destination station.

Although the embodiments of the present invention have been described inview of a process, each operation constituting the relay link setupmethod in the wireless communication system may be easily understood inview of an apparatus. Therefore, the operations included in the relaylink setup method may be understood as components included in a relaylink setup apparatus according to the principle of the presentinvention.

That is, a relay link setup apparatus according to an embodiment of thepresent invention may include a first receiving unit to receivecapability information of at least one relay supporting STA included inthe wireless communication system from an AC or a PCP, a select unit toselect one of the at least one relay supporting STA as a relay STA usingbeam forming information among the source STA, the destination STA, andthe at least one relay supporting STA and the capability information, atransfer unit to transfer an RLS request frame to the destination STA,and a second receiving unit to receive an RLS response frame thatincludes relay link setup result information from the destination STA.The RLS request frame and the RLS response frame may pass through therelay STA. Here, the relay link setup apparatus may be a source STA forperforming relay link setup in the wireless communication system.

According to another embodiment, a relay link setup apparatus mayinclude a beam forming unit to perform beam forming along with a sourceSTA, a first transfer unit to transfer channel measurement informationaccording to the beam forming performed with the source STA to thesource STA, a second transfer unit to receive an RLS request frame fromthe source STA and transfer the RLS request frame to the destinationSTA, and a third transfer unit to receive an RLS response frame thatincludes relay link setup result information from the destination STAand transfer the RLS response frame to the source STA. Here, the relaylink setup apparatus may be a relay STA for performing relay link setupin the wireless communication system.

According to still another embodiment, a relay link setup apparatus mayinclude a beam forming unit to perform beam forming along with a sourceSTA and at least one relay supporting STA, a first transfer unit totransfer channel measurement information according to the beam formingperformed with the source STA and the at least one relay supporting STAto the source STA, a receiving unit to receive an RLS request frame fromthe source STA, and a second transfer unit to transfer an RLS responseframe that includes relay link setup result information to the sourceSTA. The RLS request frame and the RLS response frame may pass throughthe relay STA selected by the source STA from the at least one relaysupporting STA. Here, the relay link setup apparatus may be adestination STA for performing relay link setup in the wirelesscommunication system.

The relay link setup method according to the foregoing embodiments maybe embodied by a computer program. A code and a code segmentconstructing the program may be easily inferred by a computer programmerhaving skill in the art. In addition, the program is recorded in anon-transitory computer-readable recording media, that is, data storagemedia, and read and executed by the computer, thereby implementing themethod. In addition, the recording media may include any type ofcomputer-readable recording media, that is, not only tangible media suchas CDs and DVDs but also intangible media such as carrier waves.

Although a few embodiments of the present invention have been shown anddescribed, the present invention is not limited to the describedembodiments. Instead, it would be appreciated by those skilled in theart that changes may be made to these embodiments without departing fromthe principles and spirit of the invention, the scope of which isdefined by the claims and their equivalents.

1. A relay link setup method of a source station in a wirelesscommunication system, the method comprising: receiving capabilityinformation of at least one relay supporting station included in thewireless communication system from an access point (AP) or a personalbasic service set (PBSS) central point (PCP); selecting one of the atleast one relay supporting station as a relay station, using beamforming information among the source station, a destination station, andthe at least one relay supporting station and the capabilityinformation; transferring a relay link setup request frame to thedestination station; and receiving a relay link setup response framethat includes information on a relay link setup result from thedestination station, wherein the relay link setup request frame and therelay link setup response frame pass through the relay station.
 2. Therelay link setup method of claim 1, further comprising transferringcapability information of the source station to the AP or the PCP,wherein the capability information comprises at least one selected fromrelay support information, relay use information, alternating current(A/C) power use information, mobility information, relay functionpreference information, relay method information, and cooperativecommunication support information.
 3. The relay link setup method ofclaim 1, wherein the receiving of the capability information of the atleast one relay supporting station comprises: transferring a relaysearch request frame for requesting the capability information of the atleast one relay supporting station to the AP or the PCP; and receiving arelay search response frame that includes the capability information ofthe at least one relay supporting station from the AP or the PCP.
 4. Therelay link setup method of claim 1, wherein the beam forming informationis obtained through scanning in units of preset sectors.
 5. The relaylink setup method of claim 4, wherein the destination station performsbeam forming along with the at least one relay supporting station andthe source station, and the selecting of one of the at least one relaysupporting station as the relay station comprises: transferring amulti-relays channel measurement request frame for requesting channelmeasurement information according to the beam forming to the destinationstation; receiving a multi-relays channel measurement response framethat includes the channel measurement information from the destinationstation; and selecting the relay station using the channel measurementinformation and the capability information.
 6. The relay link setupmethod of claim 5, wherein the channel measurement informationcomprises: channel measurement information between the source stationand the destination station; channel measurement information between theat least one relay supporting station and the destination station; andinternal angle information between a link between the source station andthe destination station and a link between the destination station andthe at least one relay supporting station.
 7. The relay link setupmethod of claim 1, wherein the relay link setup request frame comprisescapability information of the source station, the relay station, and thedestination station, association identifier (AID) information, and arelay transfer parameter, wherein the relay transfer parameter comprisesat least one selected from relay method information, cooperativecommunication use information, transfer mode information according tothe cooperative communication use, link switch section informationdenoting a link switch section, data sensing time information denoting adeferred time caused by link switching, frame exchange sectioninformation between the source station and the relay station, and frameexchange section information between the relay station and thedestination station.
 8. The relay link setup method of claim 1, furthercomprising transferring an announcement frame that includes informationon success of relay link setup to the AP or the PCP according to theinformation on the relay link setup result.
 9. The relay link setupmethod of claim 1, further comprising transferring a relay teardownframe for tearing down a relay link to the relay station, thedestination station, and the AC or the PCP, wherein the relay teardownframe comprises AID information of the source station, the relaystation, and the destination station.
 10. A relay link setup method of arelay station in a wireless communication system, the method comprising:performing beam forming along with a source station; transferring, tothe source station, channel measurement information according to thebeam forming with the source station; receiving a relay link setuprequest frame from the source station and transferring the relay linksetup request frame to the destination station; and receiving a relaylink setup response frame that includes information on a relay linksetup result from the destination station and transferring the relaylink setup response frame to the source station.
 11. The relay linksetup method of claim 10, further comprising transferring capabilityinformation of the relay station to an access point (AP) or a personalbasic service set (PBSS) central point (PCP), wherein the capabilityinformation comprises at least one selected from relay supportinformation, relay use information, alternating current (A/C) power useinformation, mobility information, relay function preferenceinformation, relay method information, and cooperative communicationsupport information.
 12. The relay link setup method of claim 10,wherein the performing of beam forming along with the source stationcomprises performing beam forming through scanning in units of presetsectors.
 13. The relay link setup method of claim 10, wherein the relaylink setup request frame comprises capability information andassociation identifier (AID) information of the source station, therelay station, and the destination station, and a relay transferparameter related to a relay link, wherein the relay transfer parametercomprises at least one selected from relay method information,cooperative communication use information, transfer mode informationaccording to the cooperative communication use, link switch sectioninformation denoting a link switch section, data sensing timeinformation denoting a deferred time caused by link switching, frameexchange section information between the source station and the relaystation, and frame exchange section information between the relaystation and the destination station.
 14. The relay link setup method ofclaim 10, further comprising: receiving a relay teardown frame fortearing down a relay link from the source station; and transferring therelay teardown frame to the destination station, wherein the relayteardown frame comprises AID information of the source station, therelay station, and the destination station.
 15. A relay link setupmethod of a destination station in a wireless communication system, themethod comprising: performing beam forming along with a source stationand at least one relay supporting station; transferring channelmeasurement information according to the beam forming with the sourcestation and the at least one relay supporting station to the sourcestation; receiving a relay link setup request frame from the sourcestation; and transferring a relay link setup response frame thatincludes information on a relay link setup result to the source station,wherein the relay link setup request frame and the relay link setupresponse frame pass through a relay station selected by the sourcestation from the at least one relay supporting station.
 16. The relaylink setup method of claim 15, further comprising transferringcapability information of the destination station to an access point(AP) or a personal basic service set (PBSS) central point (PCP), whereinthe capability information comprises at least one selected from relaysupport information, relay use information, alternating current (A/C)power use information, mobility information, relay function preferenceinformation, relay method information, and cooperative communicationsupport information.
 17. The relay link setup method of claim 15,wherein the performing of beam forming comprises performing beam formingthrough scanning in units of preset sectors.
 18. The relay link setupmethod of claim 15, wherein the transferring of the channel measurementinformation to the source station comprises: receiving, from the sourcestation, a multi-relays channel measurement request frame for requestingchannel measurement information according to the beam forming; andtransferring a multi-relays channel measurement response frame thatincludes the channel measurement information to the source station,wherein the channel measurement information comprises: channelmeasurement information between the source station and the destinationstation; channel measurement information between the at least one relaysupporting station and the destination station; and internal angleinformation between a link between the source station and thedestination station and a link between the destination station and theat least one relay supporting station.
 19. The relay link setup methodof claim 15, wherein the relay link setup request frame comprisescapability information and association identifier (AID) information ofthe source station, the relay station, and the destination station, anda relay transfer parameter, wherein the relay transfer parametercomprises at least one selected from relay method information,cooperative communication use information, transfer mode informationaccording to the cooperative communication use, link switch sectioninformation denoting a link switch section, data sensing timeinformation denoting a deferred time caused by link switching, frameexchange section information between the source station and the relaystation, and frame exchange section information between the relaystation and the destination station.
 20. The relay link setup method ofclaim 15, further comprising receiving a relay teardown frame fortearing down a relay link from the source station, wherein the relayteardown frame comprises AID information of the source station, therelay station, and the destination station.